Animation generally designates one (or more) moving images to be displayed on a screen, for example a computer screen. The animation is normally defined as a sequence of fixed images, whose regular renewal at a frequency above the sensitivity of the human eye makes it possible to simulate a movement.
In order to limit the amount of information necessary for coding these animations (in particular for their storage or transmission), it has already been proposed to completely code (according to a given algorithm) only a first part of these images (key images). For the remaining images (secondary images), there is kept (for storage or transmission) only secondary data, which allow the restoration of the initial image only with knowledge of a neighboring key image. This drawback is compensated for by the reduced size of the secondary data. Such an approach is for example used by the MPEG (Moving Picture Expert Group) standard.
It is naturally wished to transmit such animations (or sequences of images) in order to distribute them with a view to their display by one or more end users. The transmission means used has, however, a limited, and sometimes even variable, bandwidth. This is, for example, true in the case of the Internet on which the exchange of animations is expanding, especially nowadays.
It is often preferable for the user to be able to display the transmitted animation in real time or with as slight a delay as possible. In certain applications, display in real time (or almost real time) is even necessary for implementing the desired service with an acceptable quality. This is for example the case for videophone type systems in which the exchanged images of the communicating parties constitute animations.
In order to obtain a display without a sizeable delay at the end user, it has already been proposed to adapt the amount of transmitted data to the bandwidth available at transmission time. To do this, the data to be sent is first put into a hierarchy, then only part of the data (base data) or the whole of the data (base data and enhancement data), according to the available bandwidth, is transmitted. Such a solution is for example described in the patent application WO 01/03 441.